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FFT spectrum normalization

See original GitHub issue

Hello, @corbanbrook I have some question regarding the normalization of FFT results. See the link:

https://github.com/corbanbrook/dsp.js/blob/master/dsp.js#L269

Why you choose bSi = 2 / this.bufferSize? In general, to return a FFT amplitude equal to the amplitude signal which performs in FFT, need to normalize FFT data by the number of sample points. Like this:

bSi = 1 / this.bufferSize

I think it’s a bug.

Issue Analytics

State:
Created 6 years ago
Comments:5

Top GitHub Comments

2reactions

tekheddcommented, Mar 13, 2018

I also believe this is a bug. To test it empirically (hey why not), I calculated the RMS of the input signal and the RMS of the transformed signal. They should be ~equal. The default is simply wrong. If you change to 1 (or divide the magnitude of the output bins by 2) the results are correct within 5-6% for noise signals and look like a rounding error for a pure sine input.

0reactions

tpoint75commented, Oct 15, 2021

see: https://github.com/CyclotronResearchCentre/FASST/blob/master/SPTfunctions/pwelch.m#L810

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